Conventional wire rope and cable normally features a metallic core or textile core. Cable with metallic core has a disadvantage of being expensive and exceedingly heavy in long lengths. Cable with textile core of natural or synthetic fiber or yarn are normally combined and twisted together to impart various characteristics to the cable depending on the type of synthetic used. Textile core normally does not contribute to the strength of a cable but serves usually simply as a filler which keeps the cable round with the wire layers correctly spaced and supported, cushions shock loading and enhances flexibility as well as to minimize excessive friction and consequent wear of adjacent wires or strands. Textile core has a disadvantage of being normally dimensionally unstable in length, and nylon in particular is water absorbent. Even when lubricated, the ultimate elongation and tensile strength of nylon has been found to vary when used in water in response to changes in the moisture content of the nylon core.
Various attempts have been repeatedly made to combine different natural and synthetic fibers of yarns together with different types of jacket materials, e.g., plastic of different types which serve to prevent synthetic cores from having their individual filaments or strands separate and to further enhance the ability of the cable to withstand wear. Plastic impregnation of synthetic core materials is frequently employed to provide sufficient core body and to bond the core fibers. Sometimes a synthetic layer is interposed between a synthetic core fiber and the outer plastic jacket to serve as a moisture barrier. These particular specialized constructions have a disadvantage of normally undesirably restricting movement of the core fibers due to the bonded plastic coating and/or plastic impregnation of the core fibers. In addition, careful selection of a plastic jacket or sheathing must be exercised for a particular application to which the cable is to be used since certain plastics may not be compatible with the application. For example, polypropylene has a high coefficient of friction with wood and, when used as sheathing, exhibits a tendency to stick to wood so that when stressed, a rope or cable of polypropylene moves in rapid jerks causing localized frictional heating which results in rapid deterioration because of the well known low melting point of polypropylene. Accordingly, polyproplene type ropes and cables have to be provided with lubrication or other types of plastic strands to minimize the effective friction. Moreover, multi-filament fiber centers formed of polypropylene or hemp, etc., tend to exhibit substantially greater stretch characteristics and lower ultimate break strengths than wire ropes with metal cores.
It is well known to those in the art that certain types of plastic, while being adapted to a particular application, are not compatible with other types of plastic. An example is that of nylon, which is water absorbent and is not compatible with polypropylene yarns which do not absorb water; this incompatibility also exists between polyester and polypropylene yarns.
In short, problems confronting a maker of cable or rope vary significantly and are compounded with respect to the variety of available materials depending on an end use to which the rope or cable is to be applied.